Scientists from Royal Botanic Garden Edinburgh also said they had identified a previously unknown species of liverwort in Shetland.

Called Viking prongwort, it has also been found in a Norwegian fjord.

Beinn Eighe is Britain's oldest reserve, having been created in 1951. It is managed by Scottish Natural Heritage (SNH).

Liverworts thrive on cool, damp, north facing mountain slopes.

Royal Botanic Garden Edinburgh and SNH said the discoveries of the northern and Viking prongworts were exciting.

Image caption
Viking prongwort has only been found so far in Shetland and Norway

Dr David Genney, SNH's specialist on mosses and liverworts, said: "We have an amazing wealth of bryophytes - mosses and liverworts - in Scotland and some of them are found nowhere else in the world.

"Beinn Eighe in Wester Ross is the only location on Earth for Herbertus borealis - the plant's botanical name - where luckily it grows in profusion on the mountain side.

"It is a special example of the Scottish liverwort heath, a miniature forest of liverworts which grows among the heather of hills in the west Highlands."

SNH said the main threat to the plants was uncontrolled moor burning.

It said hill fires which swept through the west Highlands last spring were suspected of having harmed the globally important wildlife.

David Bell, a researcher with the Royal Botanic Garden Edinburgh, added: "This population of northern prongwort is of global importance as this is the only location it is known on Earth.

"Its closest relatives are in Asia and further research is needed to determine whether the northern prongwort has its origins in the Himalayas.

"We are fortunate that this population is so well protected on the reserve because the community as a whole is extremely sensitive to burning. We now think that the species' conservation status should be reassessed due to its rarity."